Using Aperture Impedance for Shielding Effectiveness Estimation of a Metallic Enclosure With Multiple Apertures on Different Walls Considering Higher Order Modes

In this paper, our previously published analytical method for calculation of shielding effectiveness (SE ) of a metallic enclosure with a centered aperture is extended to generalize the method for a much wider range of applications. The new extended analytic formulation considers an enclosure with centered and off-centered apertures on different enclosure walls and the monitoring point can be anywhere inside the enclosure. In addition, the incident field angle and the polarization angle are arbitrary and higher order modes are considered. An analytic discussion and an experimental setup are proposed for the validation of the new method. The proposed measurement setup can lead to a new SE measurement method for enclosures with arbitrary position apertures. In this measurement method, there is no need for antennas, reverberation chambers, etc. Another advantage of the proposed method is introducing a new figure of merit for shield evaluation. This new figure of merit is S11 of a two port microstrip line which is placed over the apertures.

I. Introduction

Electromagnetic compatibility importance increases in case of highly integrated and dense circuits and higher operating frequencies. In such situations, isolation between the individual systems becomes more important and the concept of shielding is the main concern. When there is a solid metallic shield between two mediums, the leakage of the electromagnetic shield will be reduced to an acceptable extent, but when there are some interruptions in the body of the shield, such as apertures, seals, slots, and etc., these discontinuities are the main sources of leakage and they have detrimental effects on the shield efficiency. To have a better comparison between the performances of the shields, some figures of merit have been defined. The most accepted and preferred figure of merit is shielding effectiveness (SE). The most preferred definition for SE is the ratio of the field at the point that is intended to be shielded, in the absence and presence of the shield, respectively. Since two different fields that can be measured are electric and magnetic fields, and are defined and can be expressed in “dB.” For instance, can be measured through [1]:

$$\begin{equation} {\rm{S}}{{\rm{E}}_E} = 20\;{\rm{log}}\;{E_{{\rm{abs}}}}/{E_{{\rm{prs}}}}) \end{equation}$$ where and are the electric fields in the monitor point (a point in the shielded media) in the absence and presence of the shield, respectively.